Concentric X-braced frames with HSS bracing

Concentrically braced frames are stiff, strong systems frequently used to resist wind and seismic loading; in regions of high seismicity in the US special concentrically braced frames (SCBFs) are used. CBF configurations vary, but in low rise or other structures with modest levels of demands single-story, X-configured braced frames (X-braced) are commonly used. The brace sections used also vary but hollow structural sections (HSS) are the most common in the U.S. Although important, in part because low-rise structures sustain large demands, few research programs have focused on the single-story X-brace configuration. A large research program was undertaken to understand and improve the response of SCBFs with selected testing on single-story X braced SCBFs. The test matrix consisted of two, full-scale planar X-braced frame experiments and one nearly-full-scale three-dimensional X-braced frame. The tests were designed using a new design and detailing philosophy, called the Balanced Design Method. In this paper, application of this design method to the frame is investigated, with a focus on the center-splice connection. The results show that the ultimate inelastic deformation capacity of the system is less dependent on the specific design detail at this splice. Additionally, the bi-directional load testing indicated that the out-of-plane demands did not impact the system performance.